Fastening element, particularly for blind rivets

ABSTRACT

The invention describes a fastening element ( 1 ), in particular for blind riveting, having a sethead ( 4 ), a deformation segment ( 2 ) and a shank end ( 3 ), the deformation segment ( 2 ) being arranged between the sethead ( 4 ) and the shank end ( 3 ), and the fastening element ( 1 ) being hollow inside, optionally with a mandrel ( 7 ) inside the fastening element ( 1 ), comprising a mandrel head ( 23 ) and a mandrel foot ( 24 ) tension-resistantly connected at least to the shank end ( 3 ). The shank end ( 3 ) is provided with a punch edge ( 6 ) extending essentially along the outermost periphery of the shank end ( 3 ) and formed by a peripheral surface ( 26 ) and a face ( 25 ) of the shank end ( 3 ). In the center of the face ( 25 ), a projection is provided, protruding from the plane in which the punch edge ( 6 ) lies on the side away from the sethead ( 4 ). The projection may be formed by a conical or pyramidal surface.

The invention relates to a fastening element, in particular for blindriveting, having a hollow shank comprising a sethead at its free end,having a deformation segment to form a closure head, and having aconnecting segment formed inside the shank, serving to form atension-resistant connection with a mandrel, in particular the foot of amandrel, the shank end opposed to the sethead being provided with apunch edge extending substantially along the outermost periphery of theshank and/or of the mandrel foot.

A fastening element of the kind mentioned above is described in DE 10160 771 A1.

The object of the present invention is to improve a fastening elementaccording to the prime patent with respect to its processing properties.

This object is accomplished, according to the invention, by a fasteningelement having the features of claim 1, by a fastening element havingthe features of claim 2 or a fastening element having the features ofclaim 5. Advantageous embodiments and refinements are the subject of therespective dependent claims.

The fastening element according to the invention includes a hollow shankhaving a sethead at its free end, a deformation segment to form aclosure head, a connecting segment for tension-resistant connection to amandrel arranged inside the shank, in particular the foot of a mandrel,the shank end comprising a punch edge extending essentially along theoutermost periphery of the shank, formed by a peripheral surface and aface of the shank end, and having a projection in the center of theface, protruding from the plane in which the punch edge lies, on theside away from the sethead.

Alternatively, a fastening element according to the invention, inparticular for blind riveting, is provided with a hollow shankcomprising a sethead at its free end, with a deformation segment to forma closure head, with a mandrel inside the shank comprising a mandrelhead and a mandrel foot, the foot being at least tension-resistantlyconnected to a shank end opposed to the sethead and comprising a punchedge extending essentially along the outermost periphery of the mandrelfoot, and formed by a peripheral surface and a face of the mandrel foot,and a projection being provided in the center of the face, protrudingfrom the plane in which the punch edge lies, on the side away from thesethead.

In this second alternative, the mandrel is a part of the fasteningelement, whereas in the first alternative, the mandrel may be both partof the fastening element and a part of the tool, in particular a settingdevice, and may be reused for additional setting operations.

In both alternatives for the fastening element, the conformationaccording to the invention leads to an improvement in the punching ofrivet holes in a part. The projection arranged in the face somewhatdeforms the part to be punched out before commencement of the punchingoperation, in the direction of the die serving as abutment. In this way,the pressure rise at impact of the fastening element on the work iscushioned, and the fastening element is stabilized against lateralyielding in its position relative to the work. The deformation of thework also affects the die side, and, when using a die comprising aplurality of segments movable transverse to the work, provides for animproved centering of the segments with respect to the punch edge of thefastening element. Upon the whole, the result is a better configurationof the surface of section at the work so that the surface of the shankof the fastening element then entering the punch opening is not damaged.

This is important so that the surface protection of the fasteningelement will not be impaired. Likewise, crack formation in theneighborhood of the punched hole is avoided, whereby the quality of theriveted connection is improved. The configuration of the punch edgeaccording to the invention has the further advantage that the detachedpunch scraps will not adhere to the punch edge and so are easilydisposed of.

The projection in the fastening element according to the invention ispreferably of such size and shape that the detached punch scraps willcome away automatically, and not be left adhering to the face. Theprojection may be set off from the face by a step, but the face mayalternatively make a smooth transition from the punch edge to theprojection. A conformation in which the face conforms to a conical orpyramidal surface tapering down in punch direction has proved highlyadvantageous, where the center of the face may be either flat or elsepointed.

Especially good results have been obtained when the height of theprojection, measured starting from the plane in which the punch edgelies, is 2.5% to 5% of the diameter or mean diameter of the punch edge.Further, it is advantageous if the face, at least in its regionbordering on the punch edge, and the surrounding surface, form anincluded angle from 93° to 96° with each other. By such a configuration,with no appreciable effect on the height of the punch edge, theformation of a smooth surface of section with blunt cutting edge in thework is favored.

According to a further proposal of the invention, provision may be madeso that the shank end or the mandrel foot of the fastening element,particularly in the region of the punch edge, is of greater strength, inparticular hardened. Also by this measure, in the case of partsconsisting of a stronger material, a satisfactory punch cut and a smoothsurface of section are ensured. Deformations of the punch edge, whichmay impair the punching operation, are avoided.

The fastening element according to the invention is hollow inside, sothat a mandrel may be passed through the sethead and the deformationsegment in order to achieve an at least tension-resistant connection ofmandrel foot and shank end. With the punch edge, while the fasteningelement is being pushed through a part, a hole is punched in the work.Here, of course, the punching force must be transmitted to the shank endby means of the mandrel, since the deformation segment cannot transmitthis force. Owing to the configuration of the fastening elementaccording to the invention, the punch forces acting on the work are keptsmall, and so smooth a surface of section is achieved in the work, withblunt cutting edge, that the surface of the shank entering the openingis not damaged.

Using a die to support the work during the punching operation,comprising a plurality of segments movable transverse to the work, ithas also proved advantageous that the form of the face according to theinvention serves to permit a better centering of the segment withrespect to the punch edge prior to the cutting operation.

With the fastening element according to the invention, a rivetedconnection is achieved that resembles a blind rivet connection, becausethe closure head is formed by tensile stresses. Since the punchingoperation requires bilateral access to the work, however, this is notstrictly speaking a blind riveting operation.

The deformation segment is deformed in that the shank end, with the aidof the mandrel introduced into the hollow shank, and with which atension-resistant connection with the connecting segment is produced, isdrawn in the direction of the sethead. By the deformation of thedeformation segment, a closure head is formed. With the closure head,for example two parts may be connected to each other. The deformationsegment is either made of softer material than the sethead or the shankend, or else rendered more readily deformable by suitable shaping, forexample by thinner wall thicknesses and/or apertures and/or folds in thedeformation segment.

By contrast with a punch rivet, a blind rivet will yield connectionsthat are able to assume higher tensile and shearing stresses. Besides,the punch rivet process requires ductile material on the die side, whichmust moreover have a certain minimum thickness. This is disadvantageousin mixed construction. By virtue of the invention, this advantage iscombined with the further advantage that no pre-drilled holes need besearched for into which the fastening element is to be inserted.Furthermore, any chips due to drilling the holes are avoided. Theself-punching of the fastening element achieves an inner wall providingespecially advantageous properties of the riveted connection withrespect to maximum allowable tensions and shears.

With the aid of the mandrel, firstly, the force required to punch thehole for the fastening element can be transmitted to the work; in thesecond place, with the aid of the mandrel the shank end is drawn in thedirection of the sethead. If part of the deformation segment protrudesin the rear of the work, it will be deformed by tension on the mandrel,i.e. in particular widened. If the deformation segment does not protrudein back, but is located inside the work, the deformation segment will bedeformed in the interior of the work, and by its widening will effect aclamping, i.e. in particular a positive dynamic connection betweenfastening element and part.

Advantageous embodiments of the invention will be illustrated withreference to the drawing below. The drawing is to be understood as aspecial exemplary example of the invention, not to limit the scope ofthe invention. In the drawing,

FIG. 1 shows a fastening element according to the invention, having amandrel inserted in a part;

FIG. 2 shows a procedure according to the invention, in which thefastening element, containing a mandrel, is set by a device for settinga fastening element in a part;

FIG. 3 shows a riveted connection according to the invention, theadditional part being attached to the work by means of a mandrel;

FIG. 4 shows a portion of a device according to the invention forsetting a fastening element, together with a fastening element and apart just before the fastening element is set;

FIG. 5 shows a fastening element according to the invention with amandrel having a foot on which the punch edge is configured;

FIG. 6 shows a fastening element according to the invention with aclosed bottom.

FIG. 1 shows a fastening element 1 according to the invention, having ahollow shank 27 comprising a sethead 4, a deformation segment 2 and anend 3 with punch edge 6 and an internal thread 5, into which a mandrel 7with head 23 and foot 24 is screwed. The tension-resistant connectionbetween the mandrel 7 and the shank 27 is made by a connecting segment28. The connecting segment 28 is formed by an internal thread 5 in theshank 27. The internal thread 5 is screwed into an external thread 29 onthe mandrel 7. The fastening element 1 is punched through a first part 8and a second part 9, the two parts 8, 9 having the conformation ofsheets lying one upon the other. The fastening element 1 punches its ownhole 11 through the parts 8, 9. The shank end 3 and a part of thedeformable segment 2 are located in the back 10 of the second part 9.The deformation segment 2 has a smaller wall thickness than the shankend 3. The mandrel 7 comprises a head 23 with which, firstly, additionalparts 22, as shown in FIG. 3, may be fastened, and on which the mandrel7 can be drawn in the direction of the sethead 4. The sethead 4 restsfirmly on the first part 8.

The shank 27 has a cylindrical peripheral surface 26 and, at its end 3,an annular face 25, which together form the punch edge 6. In the centerof the face 25, there is a face 32 configured on the foot 24 of themandrel. The two faces 25, 32 pass smoothly into each other and togetherform a flat conical surface, whose outward projecting point lies on thecenterline of the mandrel 7. In this way, the face 32 forms, inparticular with its tip, a projection protruding from the plane in whichthe punch edge 6 lies on the side of the fastening element 1 away fromthe sethead, and in the punching operation, strikes the work before thepunch edge 6 reaches the work. The inclination of the conical surfaceformed by the faces 25, 32 is so dimensioned that the face 25 makes anincluded angle X of 93° to 96° with the peripheral surface 26.

FIG. 2 describes a procedure of setting a fastening element 1 accordingto the invention. Into the fastening element 1, held by a holding tool13, a mandrel 7 is screwed. With the aid of moving means 19, thefastening element 1 is set on a first part 8, to be connected to asecond part 9. The position of the fastening element 1 relative to theparts 8, 9 is acquired with the aid of position-determining means 19.The parts 8, 9 are first placed on a die 14 comprising a disposalpassage 17 for parts 18 punched out. Then the fastening element 1 is soset on the first part 8 with the aid of the holding tool 13 that theshank end 3 of the fastening element 1 makes contact with the first part8 at the point of the face 32. With the aid of a stamp 12, a force isthen exerted against the parts 8, 9 on the mandrel 7, and the shank end3 is pushed through the parts 8, 9. In this operation, first the parts8, 9 are deformed in the region of the projecting face 32, and thensevered by means of the punch edge 6.

During the motion of the stamp 12, both the holding tool 13 and atension tool 15 are carried along. Punched out parts 18 drop into thedisposal passage 17 where they are then disposed of, preferably with theaid of a positive or negative air pressure line. Then the die 14 isremoved from the parts 8, 9, so that the shank end, or the projectingdeformation segment, is free. The removal of the die may be omitted ifthis is made yielding in radial direction, as shown in the prime patent.Then the tension tool 15 pulls on the mandrel 7, while the holding tool13 presses the sethead against the first part 8. The tension deforms thedeformation segment 2, whereas the shank end 3 is not plasticallydeformed. With the aid of stress sensors 21, the drawing and thepunching are monitored and the data detected by the stress sensors 21control the motion of the tension and/or the holding tool. Finally, themandrel 7 may be screwed out of the fastening element 1 or used tofasten an additional part.

FIG. 3 shows a riveted connection produced in the manner described, thefastening element 1 being deformed in its deformation segment 2. Bymeans of the mandrel 7 and its head 23, an additional part 22, which maybe a suspension, is attached to the parts 8, 9. The parts 8, 9 arefirmly clamped between the sethead 4 and the deformation segment 2.

FIG. 4 shows a detail view of the device for setting the fasteningelement 1. The fastening element 1 is held with the aid of the holdingtool 13 on the mandrel 7 screwed into the fastening element 1. Thetension tool 15 grasps the mandrel 7 by its head 23. The stamp 12presses on the head 23 of the mandrel 7. The parts 8, 9 are arrangedbetween the fastening element 1 and the die 14, the die 14 assuming,from the back 10 of the second part 9, the force exerted by the stamp 12on the parts 8, 9 by way of the mandrel 7.

FIG. 5 shows an alternative fastening element 1 a having a mandrel 7punched into two parts 8, 9. The hole 11 was punched in the parts 8, 9with the punch edge 6 configured on the foot 24 of the mandrel. Thepunch edge 6 is formed by a cylindrical peripheral surface 34 and aplane face 32 of the foot 24 of the mandrel, and has a sharp,essentially rectangular shape. In the center of the face 32, aprojection 33 set off by a step is provided, deforming the part prior tocutting. By means of the head 23, the mandrel 7 can be drawn back sothat first the deformation segment 2 is deformed and then the mandrelhead 23 parts from the foot 24 at a weak point 25. The tension-resistantconnection between mandrel 7 and shank [2]7 is made by the connectingsegment 28.

FIG. 6 shows a fastening element 1 b having a hollow cylindrical shank27 whose bore is closed by a bottom 35 at the shank end 3 opposed to thesethead 4. The shank end 3 forms a connecting segment 28 provided withan internal thread 5. The internal thread 5 serves for screwing in atool mandrel that transmits the punch force for penetrating a part andthe setting force for deforming the deformation portion 2 to thefastening element 1 b. After the setting, the tool mandrel is removedand a screw is screwed into the internal thread 5 to fasten a part. Thebottom 35 of the fastening element 1 b is provided on the outside with aconical face 25, forming an obtuse-angled punch edge 6 together with thecylindrical periphery 26. The angle of the punch edge 6 is designated byX and is preferably 93° to 96°.  1 fastening element  1a fasteningelement  1b fastening element  2 deformation segment  3 shank end  4sethead  5 internal thread  6 punch edge  7 mandrel  8 first part  9second part 10 back 11 punch hole 12 stamp 13 holding tool 14 die 15tension tool 16 abutment 17 disposal passage 18 punched out part 19moving means 20 position-determining means 21 stress sensor 22additional part 23 mandrel head 24 mandrel foot 25 face 26 periphery 27shank 28 connecting segment 29 external thread 30 closure head 31mandrel core 32 face 33 projection 34 periphery 35 bottom X angle

1. Fastening element (1), in particular for blind riveting, having ahollow shank (27) comprising a sethead (4) at its free end, having adeformation segment (2) to form a closure head, and having a connectingsegment (28) formed inside the shank (27) and serving to form atension-resistant connection to a mandrel (7), in particular the foot(24) of a mandrel (7), the shank end (3) opposed to the sethead (4)being provided with a punch edge (6) extending essentially along theoutermost periphery of the shank (27) and formed by a peripheral surface(26) and a face (25) of the shank end (3), and a projection beingprovided in the center of the face (25) protruding from the plane inwhich the punch edge (6) lies on the side away from the sethead (4). 2.Fastening element (1), in particular for blind riveting, having a hollowshank (27) comprising a sethead (4) at its free end, having adeformation segment (2) to form a closure head, having a mandrel (7)inside the shank (27), comprising a mandrel head (23) and a mandrel foot(24), the mandrel foot (24) being at least tension-resistantly connectedto a shank end (3) opposed to the sethead (4), the shank end (3)comprising a punch edge (6) extending essentially along the outermostperiphery of the shank (27) and formed by a peripheral surface (26) anda face (25) of the shank end (3), and a projection being provided in thecenter of the face (25), protruding from the plane in which the punchedge (6) lies on the side away from the sethead (4).
 3. Fasteningelement according to claim 1, characterized in that the shank end (3)opposed to the sethead (4) is open and the projection is arranged at thefoot (24) of the mandrel.
 4. Fastening element according to claim 1,characterized in that the shank end (3) opposed to the sethead (4) isclosed and forms the projection with a bottom (35).
 5. Fastening elementaccording to claim 1, characterized in that, inside the shank (27), aconnecting segment (28) is formed, serving to form a tension-resistantconnection with the mandrel (7), in particular the foot (24) of themandrel (7).
 6. Fastening element (1), in particular for blind riveting,having a hollow shank (27) comprising a sethead (4) at its free end,having a deformation segment (2) to form a closure head, having amandrel (7) inside the shank (27) comprising a mandrel head (23) and amandrel foot (24), the mandrel foot (24) being tension-resistantlyconnected at least to a shank end (3) opposed to the sethead (4) andcomprising a punch edge (6) extending essentially along the outermostperiphery of the mandrel foot (24), and formed by a peripheral surface(34) and a face (32) of the mandrel foot (24), and a projection (33)being provided in the center of the face (32), protruding from the planein which the punch edge (6) lies on the side away from the sethead (4).7. Fastening element (1) according to claim 1, characterized in that theprojection (33) is offset from the face by a step.
 8. Fastening element(1) according to claim 1, characterized in that the face (25) passessmoothly from the punch edge (6) into the projection.
 9. Fasteningelement (1) according to claim 1, characterized in that the height ofthe projection measured from the plane in which the punch edge lies is2.5% to 5% of the diameter, or mean diameter, of the punch edge. 10.Fastening element (1) according to claim 1, characterized in that theface (25, 32) has a shape conforming to a conical or pyramidal surfacetapering down in the punching direction.
 11. Fastening element (1)according to claim 1, characterized in that the cross-section of thefastening element (1) is substantially circular.
 12. Fastening element(1) according to claim 1, characterized in that the face (25) and theperipheral surface (26) make an included angle of 93° to 96° with eachother.
 13. Fastening element (1) according to claim 1, characterized inthat the cross-section of the fastening element (1) is substantiallypolygonal.
 14. Fastening element (1) according to claim 1, characterizedin that the mandrel head (23) is widened.
 15. Fastening element (1)according to claim 1, characterized in that the shank end (3) or themandrel foot (24), at least in the region of the punch edge (6), isstronger, in particular hardened.
 16. Fastening element according toclaim 2, characterized in that the shank end (3) opposed to the sethead(4) is open and the projection is arranged at the foot (24) of themandrel.
 17. Fastening element according to claim 2, characterized inthat the shank end (3) opposed to the sethead (4) is closed and formsthe projection with a bottom (35).
 18. Fastening element according toclaim 2, characterized in that, inside the shank (27), a connectingsegment (28) is formed, serving to form a tension-resistant connectionwith the mandrel (7), in particular the foot (24) of the mandrel (7).19. Fastening element (1) according to claim 2, characterized in thatthe projection (33) is offset from the face by a step.
 20. Fasteningelement (1) according to claim 2, characterized in that the face (25)passes smoothly from the punch edge (6) into the projection. 21.Fastening element (1) according to claim 2, characterized in that theheight of the projection measured from the plane in which the punch edgelies is 2.5% to 5% of the diameter, or mean diameter, of the punch edge.22. Fastening element (1) according to claim 2, characterized in thatthe face (25, 32) has a shape conforming to a conical or pyramidalsurface tapering down in the punching direction.
 23. Fastening element(1) according to claim 2, characterized in that the cross-section of thefastening element (1) is substantially circular.
 24. Fastening element(1) according to claim 2, characterized in that the face (25) and theperipheral surface (26) make an included angle of 93° to 96° with eachother.
 25. Fastening element (1) according to claim 2, characterized inthat the cross-section of the fastening element (1) is substantiallypolygonal.
 26. Fastening element (1) according to claim 2, characterizedin that the mandrel head (23) is widened.
 27. Fastening element (1)according to claim 2, characterized in that the shank end (3) or themandrel foot (24), at least in the region of the punch edge (6), isstronger, in particular hardened.
 28. Fastening element (1) according toclaim 6, characterized in that the projection (33) is offset from theface by a step.
 29. Fastening element (1) according to claim 6,characterized in that the face (25) passes smoothly from the punch edge(6) into the projection.
 30. Fastening element (1) according to claim 6,characterized in that the height of the projection measured from theplane in which the punch edge lies is 2.5% to 5% of the diameter, ormean diameter, of the punch edge.
 31. Fastening element (1) according toclaim 6, characterized in that the face (25, 32) has a shape conformingto a conical or pyramidal surface tapering down in the punchingdirection.
 32. Fastening element (1) according to claim 6, characterizedin that the cross-section of the fastening element (1) is substantiallycircular.
 33. Fastening element (1) according to claim 6, characterizedin that the face (25) and the peripheral surface (26) make an includedangle of 93° to 96° with each other.
 34. Fastening element (1) accordingto claim 6, characterized in that the cross-section of the fasteningelement (1) is substantially polygonal.
 35. Fastening element (1)according to claim 6, characterized in that the mandrel head (23) iswidened.
 36. Fastening element (1) according to claim 6, characterizedin that the shank end (3) or the mandrel foot (24), at least in theregion of the punch edge (6), is stronger, in particular hardened.